1. Field of the Invention
The present invention relates to an inner-cam type distribution fuel injection pump and, more particularly, to an inner-cam type distribution fuel injection pump actuated by an inner cam having an inner peripheral cam profile, wherein lubricating condition is improved in a cam chamber which is formed by the inner cam and a rotor rotatable in the inner cam.
2. Description of the Prior Art
Fuel economy is a current social need which has given rise to the demand for fuel injection pumps capable of injecting fuel at higher levels of pressures. To cope with this demand, in the fields of distribution type fuel injection pump for diesel engines, a pump actuating mechanism has been proposed which employs an inner cam which has an inner peripheral cam surface in place of ordinary face cam having an outer peripheral cam surface. An example of this type of fuel injection pump actuating mechanism is disclosed in Japanese Patent Unexamined Publication No. 61-96168 entitled DISTRIBUTION-TYPE FUEL INJECTION PUMP ACTUATED BY INNER CAM. This type of fuel injection pump has a rotor having a radial bore which slidably receives a plunger. As the rotor rotates, the plunger is driven by the cam profile on the inner peripheral surface of the cam so as to reciprocatingly move within the radial bore thereby sucking, pressurizing and injecting fuel. In general, the rotor can have a plurality of such radial bores and plungers so that this type of fuel injector is suitable for attaining a high fuel injection pressure. Recently, attempts have been made to use a composite fuel composed of kerosene and alcohol, instead of light oil which has been conventionally used as a diesel engine fuel oil. Obviously, a higher fuel injection pressure requires the fuel injection pump to work under severer conditions and, hence, improved durability of fuel injection pump is becoming a critical demand. More specifically, the increased fuel injection pressure of the fuel injection pump actuated by an inner cam naturally increases the pressure at which the plungers are urged against the cam profile of the inner cam, resulting in a significant increase in the load applied to the inner cam, rollers which are held in sliding contact with the inner cam and roller shoes which rotatably carry the rollers. In conventional fuel injection pumps of the type described, the lubrication in cam chamber accommodating these sliding parts has relied solely upon the fuel. Such a lubricating method, however, cannot provide a required lubricating effect particularly when the pump operates under a heavy load, i.e., at a high injection pressure. Thus, wear of the sliding parts tend to grow rapidly due to inferior lubricating condition, causing unfavorable effect on the pump characteristic and durability of the pump.